Powder and single crystal Raman spectra of the two most common phases of calcium carbonate are calculated with ab initio techniques (using a “hybrid” functional and a Gaussian-type basis set) and measured both at 80 K and room temperature. Frequencies of the Raman modes are in very good agreement between calculations and experiments: the mean absolute deviation at 80 K is 4 and 8 cm⁻¹ for calcite and aragonite, respectively. As regards intensities, the agreement is in general good, although the computed values overestimate the measured ones in many cases. The combined analysis permits to identify almost all the fundamental experimental Raman peaks of the two compounds, with the exception of either modes with zero computed intensity or modes overlapping with more intense peaks. Additional peaks have been identified in both calcite and aragonite, which have been assigned to ¹⁸O satellite modes or overtones. The agreement between the computed and measured spectra is quite satisfactory; in particular, simulation permits to clearly distinguish between calcite and aragonite in the case of powder spectra, and among different polarization directions of each compound in the case of single crystal spectra.

This paper addresses blind-source separation in the case where both the source signals and the mixing coefficients are non-negative. The problem is referred to as non-negative source separation and the main application concerns the analysis of spectrometric data sets. The separation is performed in a Bayesian framework by encoding non-negativity through the assignment of Gamma priors on the distributions of both the source signals and the mixing coefficients. A Markov chain Monte Carlo (MCMC) sampling procedure is proposed to simulate the resulting joint posterior density from which marginal posterior mean estimates of the source signals and mixing coefficients are obtained. Results obtained with synthetic and experimental spectra are used to discuss the problem of non-negative source separation and to illustrate the effectiveness of the proposed method

The vibrational properties of CaCO3 aragonite have been investigated both theoretically, by using a quantum mechanical approach (all electron Gaussian type basis set and B3LYP HF-DFT hybrid functional, as implemented in the CRYSTAL code) and experimentally, by collecting polarized infrared (IR) reflectance and Raman spectra. The combined use of theory and experiment permits on the one hand to analyze the many subtle features of the measured spectra, on the other hand to evidentiate limits and deficiencies of both approaches. The full set of TO and LO IR active modes, their intensities, the dielectric tensor (in its static and high frequency components), and the optical indices have been determined, as well as the Raman frequencies. Tools such as isotopic substitution and graphical animation of the modes are available, that complement the analysis of the spectrum.

Nanocomposites have been processed following a wet-impregnation approach, by confined growth of nanoparticles of the spin crossover complex [Fe(Htrz)₂(trz)](BF₄) within pre-formed transparent mesoporous silica monoliths of well controlled porosity. The obtained materials were studied using numerous characterisation techniques to define the interplay between the porosity of the host matrix, the structure and morphology of the in situ elaborated nanoparticles, and the spin crossover properties of the composite. Transmission electron micrographs show monodisperse spherical nanoparticles of mean diameter 3.2(5) nm, homogeneously distributed within the pores of the silica monolith. Magnetic measurements, temperature dependent infrared, Raman, and Mössbauer spectroscopy confirm the spin transition behaviour of the nanocomposite, with a room temperature bistability and 65 K wide hysteresis.

The surface properties of organosilane-modified smectite-type clays were examined by various physico-chemical techniques, including thermal gravimetric analysis (TGA), surface area measurements from N₂ adsorption/desorption experiments (BET method), Fourier transform infrared spectroscopy (FTIR), chemical stability measurements in aqueous medium, and elemental analysis. The organically modified clays derived from the reaction of two natural Cameroonian smectites and one standard bentonite sample (for comparison purposes) with γ-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane. Efficiency of the grafting process was demonstrated by comparing the physico-chemical characteristics of the clays before and after reaction with the organosilanes, which resulted in decreased porosity and decreased amounts of surface hydroxyl groups concomitantly to the presence of aminopropyl or mercaptopropyl groups attached to the aluminosilicate structure. The amine-bearing materials were subject to rather low chemical stability in neutral aqueous medium, which was improved with decreasing pH, while the thiol-containing ones were found to be stable over a wide pH range (2–10). Possible use of these materials as adsorbents for mercury(II) species was discussed and some preliminary experiments based on carbon paste electrodes modified with such grafted clays highlighted their interest for electroanalytical applications.